The present invention relates to cord for tires and radial tires for vehicles, i.e., those tires wherein the cords of the carcass plies which extend from one bead to the other lie substantially on radial planes.
Particularly, the present invention relates to light truck tires having less weight favoring low-rolling resistance to absorb less horsepower while maintaining the strength of the previous heavier construction as well as ride and handling with a simpler construction cord of greater corrosion resistance.
Assignees prior application, now published as EPO 237,462 on Sep. 16, 1987, discloses a two-ply passenger tire belt having cords of 2xc3x970.30 high tensile construction. The high tensile material used was described as high-carbon steel with a carbon content by weight of greater than 0.80%.
Co-pending with this application is Assignees U.S. application Ser. No. 07/843,133 filed Feb. 28, 1992, now abandoned disclosing 0.35 filaments both untwisted and twisted of super tensile material in a cord for a reinforcement, particularly for radial medium truck tires.
Assignees"" previous light truck tires had a common cord, 2+2xc3x970.30 high tensile for load range C and D tires, U.S. Pat. No. 5,188,685 issued Feb. 23, 1993, and 2+2xc3x970.35 ST for load range E tires, U.S. Pat. No. 5,242,001 issued Sep. 7, 1993. The present invention using 2xc3x970.35 cord, maintains a common 2xc3x97 cord for these load ranges while taking the next step forward by reducing the number of filaments in the cord from four to two. An alternate cord, 3xc3x970.35 increases the number of filaments, but reduces the required tensile strength where the tensile strength for 2xc3x97 cord would otherwise exceed what is available in current commercial materials. A key to efficient use of reinforcement is to use only as much as required by the product, but it is not always simply a matter of increasing a filament diameter to reach such a goal. Where the diameter increase still results in an unobtainable tensile strength, a filament may have to be added, or the material changed, or the ends per inch of cord changed, etc. To identify a specific type of cord for use over the widest range of variables, including use of super tensile and ultra tensile materials, it was found that the best way to illustrate the variables was graphically as in FIG. 4 below where the preferred embodiment of 2xc3x97 cord and an alternate embodiment of 3xc3x97 cord show how the variables for these cords can be brought together is illustrated.
Advantages which exist in the present cord over the previous cord include improved corrosion resistance and a weight reduction due to reduction in weight of reinforcement as well as reduction in the amount of total gum rubber gauge due to the smaller diameter of the present cord, all of which result in a reduction in cost for the tire of the present invention. Further, the new belt structure using the present cord is expected to give equal or better rolling resistance where it is recognized that the belt, even though having a smaller diameter cord, has a higher bending stiffness for the belt structure.
This invention provides the above advantages in a load range C and D pneumatic radial tire with a carcass having radial cords and two sidewalls spaced apart a distance which, in the axial direction, determines the width of the tire section. The tire has two beads each one of which around which are turned up, from the inside toward the outside, the ends of the cords of the carcass. A tread is disposed on the crown of the carcass, and a belt structure that is circumferentially inextensible is interposed between the tread and the carcass. The belt structure has a width that is substantially equal to that of the tread and has two radially overlapped layers of elastomeric fabric reinforced with metallic cords. The metallic cords are parallel to each other in each layer, which layers have a density of 28 ends per inch with a filament tensile strength of at least 3500 MPa and a 032 mm filament diameter. The cords of one layer are crossed with the other layer and inclined at an angle of between 16xc2x0 and 30xc2x0 with respect to the equatorial plane of the tire. The metallic cords being two single filaments twisted one about the other.
Further, this invention provides a pneumatic radial tire with a carcass having radial cords, two sidewalls spaced apart a distance, which in the axial direction, determines the width of the tire section, two beads each one of which around which are turned up the ends of the cords of the carcass, and a belt structure that is circumferentially inextensible interposed between the tread and the carcass, the belt structure having a width that is substantially equal to that of the tread and having at least two radially overlapped layers of elastomeric fabric reinforced with metallic cords, the metallic cords being parallel to each other in each layer, comprising at least one layer of cords comprising two filaments twisted about each other having a diameter of about 032 mm to 0.40 mm and a filament tensile strength (T) of at least T=6908-10740 (d) for a Load Range D tire.
Lastly, this invention provides a pneumatic tire with a carcass having radial cords, two sidewalls spaced apart a distance, which in the axial direction, determines the width of the tire section, two beads each one of which around which are turned up the ends of the cords of the carcass, and a belt structure that is circumferentially inextensible interposed between the tread and the carcass, the belt structure having a width that is substantially equal to that of the tread and having at least two radially overlapped layers of elastomeric fabric reinforced with metallic cords, the metallic cords being parallel to each other in each layer, comprising at least one layer of an inch strength (In.Str.) of at least 11,500 N/mm2 per in. for Load Range C wherein:
In.Str. (Newtons/mm2 per inch)=N{CE(C-2000 Newtons/mm3xc2x7d)}EPI
N=number of filaments per cord=2[OR MORE] or more
d=filament diameter=0.32 to 0.40 mm
CE=Cord Efficiency
EPI=cord end count=17 to 19 ends/inch
C=4080 to 4400 Newtons/nm2 
while for Load Range C and D the In.Str. would be at least 14,500 N/mm2 per in. and the ranges for EPI, 17-24 and C=4080 to 4400.
In further aspects of the present invention, the filament diameters of both filaments in the cord are 0.35 mm diameter and the ends per inch are 17 with ultra tensile and 19 with super tensile material for load range C tires and 21 ends per inch for ultra tensile and 24 ends per inch for super tensile for load range D tires.
The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims.